1. Field of the Invention
This invention pertains to a method of machining magnesium or other metal ingots into finely divided particulate form, and more particularly to a method of grinding successive magnesium ingots into small chips or powders without any damage to any of the grinding apparatus and without material waste. This invention also pertains to the configuration of the metal ingots used in practicing the method.
2. Statement of the Prior Art
It has been customary, when reducing magnesium or magnesium-base metals into powdered form by machining (such as disclosed in Leontis et al U.S. Pat. No. 2,657,796), to initially supply the metal in the form of ingots which are first ground into small chips by a suitable grinding machine, such as a cutter wheel. These chips may then be fed through a hammer mill where they are further reduced to powdered form. It has been found, however, that as the ingots are fed into the cutter wheel the last portion of the ingot, commonly referred to as the butt end, has a tendency to be bounced around or vibrated by the action of the cutting teeth on the cutter wheel. When subjected to such vibrations the ingot butt end sometimes slips past the cutter teeth and is removed from the grinding mechanism together with the other chips. Consequently, when the chips are fed through a hammer mill, a screen having a rather large mesh size must be employed so that any butt ends which have slipped through the initial grinder do not damage the hammer mill screen. Inasmuch as the size of the mesh is directly related to the relative fineness of the magnesium or magnesium alloy powder produced in the hammer mill, these prior art methods have only been capable of producing relatively coarse products.
Accordingly, when it is desired to reduce the magnesium to a relatively fine powdered form, it is desirable that only small magnesium chips be fed into the hammer mill in order that a screen having a relatively small mesh size may be employed therein.
One solution to this problem has been to secure the butt end of the magnesium ingot in a suitable clamping element, and then use such element to control the movement of the ingot as it is fed into the cutter wheel. However, this practice is disadvantageous in that the butt end thus clamped, which can represent as much as 5-10 percent by weight of the magnesium ingot, cannot be ground into chips without additional processing, and it is therefore normally discarded.
Another solution suggested by Dugle et al, U.S. Pat. No. 3,211,390, has been to employ ingots having a V-shaped groove at one end and a correspondingly tapered point at the other. These ingots are disposed in end-to-end relation with the tapered point of one ingot in the groove of the next and then fed into the cutting element. In conjunction with this arrangement, Dugle et al uses a plurality of spring biased guiding dogs which, together with the V-shaped groove in the front end of the succeeding ingot, serve to hold the butt end of the ingot being ground in the path of the cutter wheel. However, and as conceded by Dugle et al in their patent, even this arrangement is insufficient to accomplish complete grinding of the butt end and, therefore, Dugle et al provide a screen or trap to receive the unground butt end portions which drop out of the path of the cutter wheel. Thus, as in the case with the clamping arrangement described above, the pointed ends cannot be ground into chips without additional processing.
Accordingly, it is an object of the present invention to provide a method of grinding magnesium ingots or the like into finely divided particulate form, without any waste.
A further object of the invention is to provide a method of grinding the butt ends of magnesium ingots into small chips or powder without special processing.
A still further object of the invention is to provide an ingot having a construction particularly suited to facilitate the improved processing of the present invention.
Applicant also wishes to make of record U.S. Pat. Nos. 3,219,283, 3,373,308 and 2,279,602.